By Daniel Schweimler
BBC News, Buenos Aires
Right-wing businessman and football club president Mauricio Macri has been elected mayor of the Argentine capital, Buenos Aires.
Mr Macri's campaign focused on taxes and crime
The post is one of the most influential and sought-after in Argentina.
Mr Macri beat the government-backed left-of-centre Education Minister Daniel Filmus into a distant second place, with over 60% of the vote.
This is the worst possible outcome for President Nestor Kirchner's cabinet, with national polls due in October.
Supporters of Mr Macri began celebrating his overwhelming victory almost as soon as the polls closed.
The opinion polls had been suggesting for some time that he would beat Mr Filmus in the second and conclusive round of voting.
The question was always going to be by how much - now they have got their answer.
It is not clear whether Mr Kirchner, or his wife Christina, will stand in presidential elections in October.
But whether it is Mr or Mrs, they will now have to deal with a tough political opponent in the capital as well as thinking about the message the Argentine electorate is sending them.
It has been quite a week for Mr Macri.
On Wednesday his team, Boca Juniors, won the biggest football club competition in Latin America, and now he has clinched the mayor's post.